1. Field of the Invention
The present invention relates to an electrophotographic copying machine, an image forming apparatus such as a laser beam printer or a facsimile machine or the like, which is equipped with a sheet feeding device.
2. Related Background Art
A conventional image forming apparatus equipped with a sheet feeding device has, for instance, a structure shown in FIG. 7.
A sheet feeding cassette 101 for supporting sheets on which images are formed is mounted on a main body of the apparatus. Reference numeral 102 designates a photosensor for detecting whether or not sheets supported by the sheet feeding cassette 101 are present. When there is no sheet in the cassette 101, an actuator 102a drops to a hole part 101a provided on the bottom plate of the cassette 101, so that the photosensor 102 is turned on. Thus, the detection of no sheets on the cassette can be carried out.
Further, a cassette sensor 106 is provided for detecting whether or not the cassette 101 is mounted on the main body of the apparatus and a protruding part 101b is also provided on the cassette side corresponding to the sensor 106.
A rack 103 is formed on the lower part of the side surface of the cassette 101 and a pinion 105 driven to rotate by a motor 104 meshes with the rack 103.
In the structure described above, when all the sheets supported by the cassette 101 are fed so that there is no sheet on the cassette 101, the actuator 102a abutting on the sheets drops to the hole part 101a. Thus, the photosensor 102 interrupted by the actuator 102a is turned on, so that no sheet is detected. When the motor 104 is rotated counterclockwise for a prescribed time under this condition, the cassette 101 is automatically drawn out from the apparatus on which it is mounted because of the engagement of the rack 103 with the pinion 105. Thus, it can be recognized at a glance that the sheets are used up, and hence a user near the apparatus can be notified of a supply of more sheets to the cassette.
However, there have been encountered problems mentioned below in the above described prior art.
Specifically, since the conventional apparatus is designed to drive the motor 104 to automatically draw out the cassette 101 after the detection of no sheets on the cassette 101, the motor for drawing out the cassette 101 needs to be provided. Besides, as transfer members for transferring the driving force of the motor to the cassette 101, members such as the pinion 103 or the rack 105 must be provided.
Further, since a mounting detection sensor for detecting whether or not the sheets are housed in the cassette 101 needs to be provided, it is necessary to provide two sensors including the former sensor and the cassette sensor 106 for detecting whether or not the cassette is mounted on the main body of the apparatus.
Still further, since the frequency of operations for drawing out the cassette 101 from the apparatus is not more than that of ordinary image forming operations and the cassette 101 on which a large quantity of sheets are stacked has been mainly employed on the latest image forming apparatus, the frequency of supply of sheets to the cassette 101 is further reduced as compared with that of the prior art.
Therefore, the provision of the motor for drawing out the cassette 101 as well as the driving motor of the apparatus and the two sensors disadvantageously causes the number of parts to be increased and the cost of assembly to be increased, which would constitute a major factor to increase the cost of a product.
The present invention is devised by taking the above described problems into account and it is an object of the present invention to provide a sheet feeding device with a more simplified structure in which a user can readily supply sheets when the sheets supported by a sheet supporting means are used up in the supporting means, and an image forming apparatus provided with the sheet feeding device.